2-Alkyl-2,3-dihydro-1H-benze!indene-1-one derivatives are interesting intermediates in the preparation of metallocenes, which are applied as catalysts in the manufacture of high-molecular weight polyolefins with high isotactic properties. Various methods for the preparation of 2-alkyl-2,3-dihydro-1H-benze!indene-1-one derivatives are known in the art. For instance, U. Stehling et al., Organometallics, Vol. 13 (3), 964-70 (1994) disclose a method in which naphthalene is condensed with 2-bromo-2-methylpropanoyl bromide. The method provides a mixture of 2,3-dihydro-2-methyl-1H-benze!indene-1-one and 1,2-dihydro-2-methyl-3H-benze!indene-3-one. Drawbacks of this method are the relatively low yield (74%) and the mixture of benze!indene isomers which is obtained and which can only be separated and purified by expensive column chromatography. This means that in follow-up steps also mixtures are obtained, and that the final product must be purified of its contaminants, which is a laborious and expensive procedure.
J. R. Merchant and R. B. Upasani, Chem. Ind., 929 (1983), prepared a mixture of benze!indene-1-one and benze!indene-3-one derivatives from 1,6-dimethoxynaphthalene and acrylic acid in the presence of polyphosphorous acid, which mixture was not separated.
In a method disclosed in U.S. Pat. No. 5,455,366, 2-methyl-3-naphthylpropionic acid was cyclized using thionyl chloride. This method does not lead to a mixture of isomers, but it has the disadvantages that expensive silica gel chromatography purification is necessary and that unacceptably low yields are obtained (45%). Other known methods suffer from one or more of the same drawbacks, i.e. low yields, laborious and expensive purifications, and the occurrence of mixtures of isomers.
Many methods for obtaining 1-indanone and derivatives thereof have been disclosed. However, because ring closure of phenylpropanone or derivatives thereof usually does not give rise to a mixture of isomers, these methods do not give any indication of the selectivity of such reactions. Moreover, the few methods for the synthesis of indene derivatives from substituted phenyl derivatives which have been disclosed, also lead to mixtures. For instance, EP 629,631 describes the ring closure of p-cymene with 2-methyl-2-propenoyl chloride, which leads to a mixture of isomers in a low yield (67%). The respective .alpha. and .beta. positions in naphthalene are the reason for the occurrence of a mixture of isomers.
The present invention therefore provides a novel method circumventing all of the above-mentioned disadvantages. In its most general concept, the invention concerns a process of preparing a 2-alkyl-2,3-dihydro-1H-benze!indene-1-one derivative, characterized in that a naphthalene derivative is condensed with an active ester of 2-alkyl-2-propenoic acid. The method provides a high yield, a better than 95% selectivity, and a simple and inexpensive purification method by crystallization.